An electrorheological (ER) fluid generally comprises ER particles suspended in an electrically insulating fluid. ER fluids are very well-known and do not need to be described in detail here. Such fluids have the property that the rheological characteristics of the fluid can be controlled by applying an electric field. In particular upon application of an electric field the viscosity of the fluid increases, and this property can be used in a number of applications so that upon application of an electric field the fluid can, for example, either (a) offer resistance to shear, (b) offer resistance to flow, or (c) offer resistance to bending distortion.
However, it is often the case that in ER applications providing shear resistance, the shear resistance will decrease with increasing shear rate, so that at high shear rates the resistance is minimal, i.e., the ER fluid would lose its effectiveness. This is a well-known generic problem. Similar problems would happen when ER fluids are used to provide flow resistance when the flow rate is high. For ER applications intended to provide resistance to bending distortion, while there can indeed be resistance to bending distortion, the stiffness that results is usually not high enough for many applications.